A pump jack system, which is known by several different names (beam pumping, pumping units, rocking horse, oil jack, jack pump, and many others) are above ground units that are used to drive for a reciprocating piston pump in an oil well that is located downhole in the bore of a subterranean formation. The pumping action is used to mechanically lift well bore fluids from the well bore to the surface. The pumping unit operates electrically, whether through standard power or gas generated powered prime mover which turns the crank and moves the pitman arms in a pivoting vertical motion. This motion moves the walking beam in proportion to the amount of adjustable movement of the pitman arms. The horsehead attaches to the walking beam over the well head. Suspended from the horsehead is the bridle. The polish rod has a polish rod clamp attached to it that holds the position of the rod string. The clamps sit on top of the carrier bar. The polish rod goes through the stuffing box and is attached to the rest of the subsurface rod string which is attached to the downhole pump. This positioning of the parts allows the mechanical vertical movement of the pumping unit to be transferred to the rod string and to the down pumping system. The process of creating the downhole motion of the pumping system can also be created by the use of a vertically mounted hydraulic pumping system. The hydraulic system, though different on the surface, creates the same motion to the downhole system.
The bottom of the well may be a considerable distance from the surface, necessitating the use of a string of sucker rods. The string length/stretch typically changes due to the level of fluid in the well, i.e., the buoyancy effect on the rods. In the course of each day, continually changing conditions affect the overall length of the string of sucker rods, causing the string to increase or decrease in the length. The change in the length is not entirely predictable. The sucker rods also tend to stretch under operating loads over long periods. Other considerations are that the required adjustment range increases with well depth.
In order to ensure full pump fillage and improve production efficiency, the pump stays in the same position in relation to the valve clearance. The pump's plunger should be as close to the bottom of the pump as possible to ensure maximum pump fillage. The pump should be present as close to the bottom of the well as possible, which may result in “the coupling that attaches the pull rod of the pump to the rod string contacting the top of the pump during the downstroke. This contact of the coupling and the top of the pump is known in the industry as tagging. This action of tagging causes many destructive effects. It increases the stress on the entire sucker rod string. It also causes the sucker rods to buckle and slap the inside of the tubing, which causes increased wear to the sucker rods and the tubing, and begins to start the fatigue process on the rod string. Therefore, a compensating adjustment is needed from time to time.
The pump used in connection with the sucker rods can undergo “gas lock”. “Gas lock” occurs when gas enters the area below the plunger when the plunger is at the uppermost position of travel and while traveling to its lowermost position, cannot compress the gas sufficiently to force the traveling valve open. On the following upstroke, the gas expands and keeps the pressure high enough below the plunger so that the standing valve will not open and allow fluid to enter the pump. This compressing and expanding of gas repeats itself on each downstroke and upstroke without increasing pressure enough to open the traveling valve or decreasing pressure enough to allow the standing valve to open and allow fluid to enter the pump. The simple solution to this problem is to periodically adjust the stroking depth of the plunger in the pump by adjusting the rod string. The “lowering” of the rod string can create enough pressure inside the pump to force the valve to open. The lowering of the rod string can also be moved enough so that the coupling on the pull rod strikes the top of the pump. This causes vibration in the pump and may shake the traveling valve to allow the gas to escape into the tubing to reduce the “gas lock” condition.
To avoid damage to sucker rods and lost production, the depth of the sucker rod string in the well should be controlled by lowering or raising the sucker rod string to either stop gas lock or to prevent tagging. Tagging is prevented while at the same time maximum pump fillage is ensured because the plunger is fully engaged. There have been efforts to address this task, one approach outlined by Norman (U.S. Pat. No. 5,101,676) is to provide a sucker rod depth adjusting attachment which comprises a cross bar and supporting underslung solid piston rams on each side thereof. The upper piston ends of these rams abut a depth adjusting bar, which is adjustably positioned above the cross bar by extension or retraction of the ram.
There are currently only manual solutions for spacing the sucker rod string, i.e., lowering or raising the sucker rod string. The existing manual devices to space the sucker rod string are tedious and require someone to be onsite to make the adjustments. The manual devices are not designed to constantly monitor the position of the plunger and to make automatic adjustments to ensure complete pump fillage without tagging. In addition, by the time someone realizes that a sucker rod string is tagging and makes the adjustment, the damage to the equipment has likely already occurred.
There exists a need for a device to monitor and adjust the depth of a sucker rod string automatically.